The present technology relates to an electrophoretic element including an electrophoretic particle and a porous layer, and a display device including the electrophoretic element.
In recent years, a demand for a display device with low power consumption and high-grade image quality has been increased as a result of widespread use of mobile devices typified by a mobile phone or a personal digital assistant (PDA). In particular, an electronic book terminal for reading application in order to read character information for a long time is recently noticed as a result of launch of the distribution service of the electronic books, leading to a demand for a display having a display grade suitable for such an application.
A cholesteric liquid crystal display, an electrophoretic display, an electrochromic display, or a twist-ball display have been proposed as the reading display. In particular, a so-called reflective-type display is preferable. This is because the reflective-type display performs light display on the basis of reflection (scattering) of outside light as in paper, leading to a display grade similar to paper. Moreover, the display need not include a backlight, leading to reduction in power consumption.
A prominent candidate of the reflective-type display includes the electrophoretic display that creates light and darkness (contrast) on the basis of an electrophoretic phenomenon. This is because the electrophoretic display is low in power consumption and fast in response. Thus, various investigations have been made on a displaying method of the electrophoretic display.
Specifically, a method has been proposed, in which two types of charged particles, which are different in optical reflective characteristics and in a polarity, are dispersed in an insulating liquid, and the respective charged particles are moved depending on an electric field on the basis of such a difference in the polarity (for example, see Japanese Examined Patent Application Publication No. 50-015115 and Japanese Patent No. 4188091). In this method, distribution states of the two types of the charged particles are differently changed depending on the electric field, creating a contrast due to such a difference in the optical reflective characteristics.
In addition, another method has been proposed, in which charged particles are dispersed in an insulating liquid, and a porous layer, which has a different optical reflective characteristics from those of the charged particles, is provided to move the charged particles through pores in the porous layer depending on an electric field (for example, see Japanese Unexamined Patent Application Publication No. 2005-107146, Japanese Examined Patent Application Publication No. 50-015120, Japanese Unexamined Patent Application Publication No. 2005-128143, and Japanese Unexamined Patent Application Publication No. 2002-244163). For the porous layer, a polymer film having pores formed by laser drilling, a synthetic fiber woven fabric, a open-cell porous polymer, or the like is used. In this method, a distribution state of the charged particles is changed depending on the electric field, leading to a contrast due to such a difference in the optical reflective characteristics between the charged particles and the porous layer.
Still another method has been proposed, in which charged particles are enclosed in microcapsules, or a partition structure is provided to define areas in which the charged particles may exist (for example, see Japanese Patent No. 2551783 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2003-526817). This method suppresses agglomeration, precipitation, convection, and the like of the charged particles.